Abstract

I review recent progress and challenges in studies of the earliest galaxies, seen when the Universe was less than 1 billion years old. Can they be used as reliable tracers of the physics of cosmic reionization thereby complementing other, more direct, probes of the evolving neutrality of the intergalactic medium? Were star-forming galaxies the primary agent in the reionization process and what are the future prospects for identifying the earliest systems devoid of chemical enrichment? Ambitious future facilities are under construction for exploring galaxies and the intergalactic medium in the redshift range 6 to 20, corresponding to what we now consider the heart of the reionization era. I review what we can infer about this period from current observations and in the near-future with
existing facilities, and conclude with a list of key issues where future work is required.

I acknowledge valuable discussions with my co-Rapporteur, Steve Furnaletto, a colleague on the Hubble Ultra Deep Field (UDF) campaign. I likewise acknowledge the support and scientific input from my other UDF colleagues, Brant Robertson, Jim Dunlop, Ross McLure and Anton Koekemoer, as well as my Keck spectroscopic co-workers Dan Stark, Matt Schenker, Tucker Jones and Adi Zitrin. I thank the organizers of this memorable meeting for their organizational efforts and hospitality in Brussels.